1. Field of the Invention
The present invention is concerned with a road-paving vehicle such as asphalt finisher, repaver or remixer which paves the road with a composite material. More specifically, the invention relates to a screed device in a road-paving vehicle such as asphalt finisher equipped with an extensible screed capable of extending the paving width to about three times as large as the width of a main screed.
2. Prior Art
Referring to FIG. 8, an asphalt finisher 1 is equipped with a hopper 2 for receiving composite material from a dump truck, and a conveyer-bar-feeder 3 for conveying the composite material in the hopper 2 to the rear side (toward the front in the drawing). The composite material conveyed to the rear side by the conveyer-bar-feeder 3 falls on the road and is conveyed in the direction of width of pavement by a screw spreader 4 installed at the rear part of the main body of the asphalt finisher 1. At the back of the screw spreader 4, the composite material is paved by a screed device 6 coupled by screed arms 5 to the main body of the asphalt finisher 1.
According to the conventional screed device 6 capable of changing the width of pavement, a main screed 7 is provided, at the back or in front thereof, with extensible screeds 8, 8 having a width of about one-half the width of the main screed 7 on the right and left sides, respectively, and these extensible screeds 8, 8 are moved in the directions of width of pavement but opposite to each other by the feeding or extending devices such as hydraulic cylinders or threaded rods that are not shown in order to extend the width of pavement.
During the execution of works, the screed arms 5 move up and down causing the paving angle to change due to the holding amount of the composite material or due to various factors, and the height of the rear end of the lower surface of the main screed 7 becomes no longer in agreement with the height of the rear end of the lower surface of the extensible screeds 8. Accordingly, stripes are formed on the paved surface 9 (FIG. 9) due to a step between the main screed 7 and the extensible screeds 8. To prevent this, the extensible screeds 8 are moved up or down relative to the main screed 7, or the step is adjusted between the main screed 7 and the extensible screeds 8 depending upon a change in the paving angle, so that the rear end of the lower surface of the main screed 7 and the rear end of the lower surface of the extensible screeds 8 acquire the same height from the paved road surface 10.
The operation for paving the composite material can be finished within a shortened period of time if the total width of the screed device 6 is increased to extend a range of pavement. In order for the asphalt finisher to be transported by using a truck, however, the minimum width of the screed device 6 (nearly the same as the main screed width L (FIG. 8)) is limited to be not wider than the width of the rear body of the truck. With the constitution shown in FIG. 8, therefore, the range L max of pavement is smaller than two times the width L of the main screed at the greatest. In order to execute the pavement maintaining a range which is in excess of two times width L of the main screed, therefore, it becomes necessary to attach extension screeds 12, 12 (FIG. 11) to the outer ends of the extensible screeds 8, 8 by using bolts or by utilizing hinges, or it becomes necessary as shown in FIG. 10 to provide extensible screeds 11, 11 that can be extended and contracted by the feeding or extending devices such as hydraulic cylinders that are not shown at the back on in front of the extensible screeds 8, 8 provided at the back or in front of the main screed 7 like a screed apparatus disclosed in Japanese Unexamined Patent Publication (Kokai) No. 102521/1995.
Referring to FIG. 12, furthermore, extensible screeds 13 and 14 having a width nearly equal to the width of the main screed 7 are provided in front and at the back of the main screed 7, and are extended in the directions opposite to each other by the feeder devices such as hydraulic cylinders that are not shown in order to extend the range of pavement to be more than two times the width L of the main screed (FIG. 12).
When the extensible screed 11 is provided at the back or in front of the extensible screed 8. of FIG. 10 as shown in FIG. 13, steps must be adjusted so that the rear end of the lower surface of the extensible screed 8 and the rear end of the lower surface of the extensible screed 11 acquire the same height from the paved road surface 10 and, hence, the adjustment must be effected at a total of four places on the right side and the left side. The operation for adjusting the steps requires a considerable time, laborious work and a high degree of skill.
Next, when the extension screeds 12, 12 are attached by bolts to the outer ends of the extensible screeds 8, 8 as shown in FIG. 11, the extension screeds 12 become heavy, and considerable work and time are required for the attachment and detachment before executing the work and before the transportation. Further, a skill is required for adjusting the lower surfaces of the extension screeds 8 to be in match with the lower surfaces of the extension screeds 12.
It was described above that the paving angle of the screed device changes depending upon the holding amount of the composite material. However, the paving angle of the screed device is further affected by the holding amount of the composite material in front of the main screed 7. A change in the paving angle of the screed device results in a change in the thickness of pavement. To execute the pavement maintaining a predetermined thickness, therefore, the paving angle must be maintained as constant as possible during the execution of works. In the case of the screed device shown in FIG. 12, however, the holding amount of the composite material in front of the main screed 7 changes depending upon the amount of extension of the extensible screed 13 in front of the main screed 7. Therefore, the paving angle of the screed device is not maintained constant, making it difficult to execute the pavement maintaining the predetermined thickness.
In order to solve the above-mentioned problems, there has been proposed a screed device as taught in Japanese Patent Application No. 155974/1998 (referred to as prior application) (see FIG. 14) filed by the present applicant, according to which extensible screeds 15, 16 having a width nearly the same as the width of the main screed 7 are arranged in a pair back and forth at the back of the main screed 7, holes that are not shown are perforated in instruction arms 17, 18 protruding from both sides at the rear upper portions of the main screed 7, guide shafts 19 and 20 are slidably supported thereby, both ends of the guide shafts 19 and 20 are secured to both ends of the extensible screeds 15 and 16, feeding or extending devices such as hydraulic cylinders that are not shown are provided at the upper portions of the main screed 7 in the directions opposite to each other, and the extensible screeds 15 and 16 are moved by the feeding or extending devices from the rear positions of the main screed in the directions of pavement but opposite to each other, in order to extend the range of pavement to be about three times as large as the width L of the main screed.
In order to broaden the range of pavement even by a small amount, however, the width of the instruction arms 17 and 18 must be narrowed, whereby the width for supporting the guide shafts 19, 20 becomes narrow making it difficult to maintain rigidity of the screed device. In executing the works, therefore, both ends of the extensible screeds 15, 16 jump up from the paved surface due to the reaction, and the thickness of pavement does not become constant in the direction of width of pavement.
Referring to FIG. 15, the composite material sent in the direction of width of pavement by the screw spreader 4 is placed in front of the main screed 7 and the extensible screeds 15, 16 as the asphalt finisher 1 proceeds. However, the extensible screeds 15, 16 located behind the main screed 7 hold more composite material, and most of the composite material stays thereon.
The asphalt finisher 1 proceeds holding large amounts of the composite material and, hence, requires a large driving force (engine output) consuming fuel in an increased amount. Further, since the extensible screed 16 is behind the extensible screed 15, resistance due to the holding amount of the synthetic material differs depending on the right side and the left side, and it becomes difficult for the asphalt finisher 1 to proceed straight.
Further, the composite material that is staying is cooled and is solidified, and is discarded after the end of the paving work and is thus wasted. Further, as the composite material 21 that is cooled and solidified falls on the paved surface 9, there develops inconvenience 22 called xe2x80x9cdragging holesxe2x80x9d on the paved surface requiring additional time for the repair work, which becomes a burden for the workers (FIGS. 16(a) and 16(b)).
It is therefore an object of the present invention to provide a screed device in a road-paving vehicle such as asphalt finisher, capable of steplessly changing the width of pavement up to about three times the width of the main screed through a simple operation.
(1) The screed device of the present invention is so constituted that a pair of extendable or extensible screeds 15, 16 having a width or length nearly equal to the width or length of a main screed are arranged back and forth at the back of the main screed 7 in the direction of progress, wherein supports 27, 28 are allowed to move in the direction of width of pavement being supported by support portions 23, 24 provided on both sides at the rear upper portions of the main screed 7, said extensible screeds 15, 16 are supported by said supports 27, 28 so as to be freely moved in the direction of width of pavement, and said extensible screeds 15, 16 are moved by the feeding or extending devices such as hydraulic cylinders in the directions of width of pavement but opposite to each other from the rear positions of the main screed 7.
(2) The support portions 23, 24 are supported to move up and down with respect to the main screed 7 by hoist means such as threaded rods 29 to adjust the steps between the extensible screeds 15, 16 that are movable in the direction of width of pavement.
(3) The extensible screeds 15, 16 are divided into upper frames 16a, 16a and lower frames 15b, 16b, and the lower frames 15b, 16b are caused by hoist means 30 such as hydraulic cylinders to move up and down relative to the upper frames 15a, 16a that move in the direction of pavement thereby to adjust the step between the extensible screeds 15 and 16.
(4) An extensible molding board 32 coupled at its one end to a side arm 31 extending forward in the direction of progress from an outer end of the rear extensible screed 16, is supported by a guide 33 provided on the rear surface of the main screed 7 so as to freely move in the direction of width of pavement along a surface nearly the same as the rear surface of the main screed 7 (front surface of the front extensible screed), thereby to adjust the height of the lower end of the extensible molding board 32, so that the composite material is placed in an amount required for the pavement in front of the rear extensible screed 16.
(5) Extensible molding boards 36, 37 coupled at their ends on one side to side arms 34, 35 extending forward in the direction of progress from the outer ends of the extensible screeds 15, 16, are supported by guides 38, 39 provided on the front surface of the main screed 7 so as to freely move in the direction of width of pavement along a surface nearly the same as the front surface of the main screed 7, thereby to adjust the heights of the lower ends of the extensible molding boards 36, 37, so that the composite materials are placed in amounts required for the pavement in front of the extensible screeds 15, 16.